1. Field of the Invention
The invention relates to an improvement of a charging apparatus for charging a photosensitive member in the electrostatic recording equipment.
2. Description of the Prior Art
An image generating section of the electrostatic recording equipment such as electrophotographic reproducing machines uses a charging apparatus that incorporates slender discharging wires as electrodes.
The charging apparatus has an elongate frame of shielding member in which discharging tungsten wires, each several tens of microns in diameter, are stretched and applied with high voltages to produce corona discharges to apply charges to the photosensitive member. As is known, the wires easily accumulate toner particles, paper particles or other solid material of oxide layers and these accumulated foreign matters will disturb uniform distribution of intensity of charges, resulting in uneven density of copied images.
For this reason, the charging apparatus requires a cleaning device to clean the discharging wires. Generally, the wires are cleaned over the entire length by sliding the cleaning member supported on the shield member to rub the wires.
In the charging apparatus with two discharging wires, it is advantageous that the cleaning member be supported on a back plate which forms a back portion of the shielding member. Thus, the back plate has an elongate opening in which the cleaning member is supported and inserted.
However, in the shielding member of the above structure in which the opening is formed in the back plate to encourage discharging from the wires to the back plate, there is a problem that an increased discharging to the back plate will result in lightnings to the edges of the opening, disturbing effective discharging to the photosensitive member. On the other hand, when, to avoid this undesired phenomenon, more charges are made to reach the side plates with no opening--which form the side portions of the shielding member--than the back plate, the ion flow toward the photosensitive member and the ion flow toward the side plates combine to increase the corona winds which in turn disperse toner particles removed from the photosensitive member, disturbing the copied images or contaminating the interior of the equipment.
In the charging apparatus in Japanese Patent Laid-Open No. 62-86,375 a shielding member and a cleaning device for cleaning a discharging wire are provided. In said apparatus on the back plate of the shielding member, no opening for supporting and guiding the cleaning member is provided, but guide rails are provided to guide the cleaning member. Further, means for rotating the cleaning member in the guide rails is provided to separate the cleaning member from the discharging wire. Accordingly, the charging apparatus becomes complicated in construction and the cleaning member is unstable in the cleaning operation because it may be rotated in the guide rails inadvertently.
In the charging apparatus in Japanese Utility Model Laid-Open No. 50-73,440, an elongate opening is provided on the back plate. However, a special means for separating a cleaning member from a discharging wire is provided so that the charging apparatus becomes complicated in construction.